The present invention broadly relates to Local Area Networks and, more specifically, pertains to a new and improved method and arrangement for transmitting data in a data loop having at least two successively arranged stations.
Generally speaking, the method of the present invention is for transmitting data in a data loop having at least two successively arranged stations optionally provided with peripheral devices, at least one of which is an overriding master station, and comprises the steps of: generating in the overriding master station transmission frames for data to be transmitted; the step of generating transmission frames entailing generating transmission frames which are partitioned into time slots, preferably equally great time slots, and with a predetermined constant number of clock cycles; and this step of generating transmission frames also entailing generating transmission frames for containing successive data to be transmitted in mutually immediate succession such that the termination of each transmission frame of the transmission frames is followed by the beginning of a subsequent transmission frame of the transmission frames.
The arrangement of the present invention is for transmitting data in a data loop wherein the data loop comprises at least two stations interconnected by a data transmission medium, such as cables, transmitter devices, optical conductors, electrolytes or the like, forming a closed loop, at least one station of the at least two stations being an overriding master station, the overriding master station comprising a generator for generating transmission frames, the at least one overriding master station comprising a transmitter device for entering the transmission frames into the data loop or into the medium interconnecting the at least two stations; the data transmission medium conducting the transmission frames through all stations and back to the overriding master station; each station of the at least two stations, inclusive of the at least one overriding master station, comprising a receiver device for the transmission frames, a synchronization device and at least one input-output device or input-output device port; each station being associated with at least one peripheral device; each input-output device or input-output device port serving selectively either for transferring data being transmitted and contained in a predetermined data-receive position in each transmission frame to the peripheral device or for inputting data to be transferred from the peripheral device into a predetermined data-transmit position in each transmission frame; the data loop defining a direction of data transmission; and each station comprising a transmitter unit arranged subsequent to the input-output device or input-output device port in the direction of data transmission for transferring or entering transmission frames into the data transmission medium, possibly with the data to be transmitted in altered form.
Data networks normally have the form of "point to point" connections between nodes or points of intersection or, alternatively, the form of several stations, only one of which is permitted to transmit at one time, are simultaneously connected to one common data transmission medium (cable, radio.) Information is normally serialized and transferred or transmitted in blocks or packets. Communication between stations is always regulated by a network-specific protocol or set of procedural rules. Such protocols are, for instance, X.25 of the CCITT, Ethernet, ISO-P 802 and the like.
With the exception of time-segmented or multiplexed connections or circuits, the transmission of data requires the control of network access or priority arbitration, which calls for a certain expenditure of time and is done on the basis of addresses and arbitration priority codes contained in the transmission framing. This, for instance, is also the case in the German Patent Publication No. 2,612,311 which describes a comparable device.
Each transfer unit or each transmission frame (information block or data packet) requires a synchronization operation whose time overhead is fully integrated into the transmission time.
All protocols transmitted contain parity-checking or redundancy-checking mechanism (for instance Cyclic Redundancy Checking or LRC, VRC) for detecting transmission errors. Upon detection of transmission errors, information blocks are repeated.
Due to fluctuating network loads and consequently different arbitration rates as well as to possible repetitions for correcting transmission errors, unpredictable transmission delays are caused in all known Local Area Networks. As a consequence, these Local Area Networks or LAN's cannot be used in time-critical real time applications and control loops or circuits.
The development or evolution of data processing installations into locally distributed systems with central data banks and the necessity to communicate with distant peripheral equipment even some years ago gave rise to nearly hopeless cabling problems. The often required flexibility could not satisfactorily be assured by the technique of individual cabling.
Based on the typical structure and distribution of data processing units, the following requirements are imposed on a data network:
(a) standard interfaces (e.g. V24 asynchronous) are to be provided on the equipment interconnections; PA0 (b) each physical connection in the data network is to be connectable to any other connection with a minimum of manipulation. The high flexibility and easy configurability required for this are to be achieved by implementation of permanent or dedicated lines, on the one hand, while the implementation of temporary connections without interruption of network operation should be possible, on the other hand. PA0 (c) Many available data or communication channels of medium data rate as well as high speed data or communication channels should be implementable at freely selectable data rates on the equipment interfaces. PA0 (d) Protocol transparency is desirable, which means that each end to end log should be implementable in the data loop, the data loop should behave like a physical connection (no store and forward operation) and moreover, the system should be absolutely insensitive to transmission control characters. PA0 (e) High reliability and low residual error rate by use of an optical medium (galvanic decoupling between the individual loop stations), error detection, error localization and diagnosis up to the equipment interface as well as central documentation of all errors and operational failures should be possible.
Control of the connection circuit or routine should be possible either by means of a central routing processor or by intelligent equipment interfaces or manually from each station (routing units).